Electrical fuse having sublithographic cavities thereupon

ABSTRACT

An electrical fuse and a first dielectric layer thereupon are formed on a semiconductor substrate. Self-assembling block copolymers containing two or more different polymeric block components are applied into a recessed region surrounded by a dielectric template layer. The self-assembling block copolymers are then annealed to form a pattern of multiple circles having a sublithographic diameter. The pattern of multiple circles is transferred into the first dielectric layer by a reactive ion etch, wherein the portion of the first dielectric layer above the fuselink has a honeycomb pattern comprising multiple circular cylindrical holes. A second dielectric layer is formed over the circular cylindrical holes by a non-conformal chemical vapor deposition and sublithographic cavities are formed on the fuselink. The sublithographic cavities provide enhanced thermal insulation relative to dielectric materials to the fuselink so that the electrical fuse may be programmed with less programming current.

FIELD OF THE INVENTION

The present invention relates to semiconductor structures, andparticularly to an electrical fuse having sublithographic cavities upona fuselink portion thereof and methods of manufacturing the same.

BACKGROUND OF THE INVENTION

Electrical fuses (eFuses) are used in the semiconductor industry toimplement array redundancy, field programmable arrays, analog componenttrimming circuits, and chip identification circuits. Once programmed,the programmed state of an electrical fuse does not revert to theoriginal state on its own, that is, the programmed state of the fuse isnot reversible. For this reason, electrical fuses are calledOne-Time-Programmable (OTP) memory elements.

The mechanism for programming an electrical fuse is electromigration ofa metal semiconductor alloy induced by an applied electrical field and araised temperature on a portion of the electrical fuse structure. Themetal semiconductor alloy is electromigrated under these conditions fromthe portion of the electrical fuse structure, thereby increasing theresistance of the electrical fuse structure. The rate and extent ofelectromigration during programming of an electrical fuse is dependenton the temperature and the current density at the electromigratedportion.

An electrical fuse typically comprises an anode, a cathode, and afuselink. The fuselink is a narrow strip of a conductive materialadjoining the anode and cathode. During programming of the electricalfuse, a positive voltage bias is applied to the anode and a negativevoltage bias is applied to the cathode. As electrical current flowsthrough the fuselink having a narrow cross-sectional area, thetemperature of the fuselink is elevated. A high current density combinedwith the elevated temperature at the fuselink facilitateselectromigration of the conductive material, which may comprise a metalsilicide.

In general, the higher the temperature of the fuselink, the easier it isto electromigrate the conductive material, i.e., the less current isneeded to induce electromigration. Since programming of electrical fusestypically takes a substantial amount of current, for example, aprogramming current of about 5 mA for an electrical fuse having afuselink width of about 63 nm, it is advantageous to provide effectivethermal isolation to the fuselink to keep the temperature of thefuselink elevated during the programming.

While fuselinks of conventional electrical fuses are insulated bydielectric materials so that heat loss from the fuselink is containedduring programming of the electrical fuse, improved thermal isolation ofthe fuselink and a higher temperature during programming would reducethe amount of electrical current needed for programming the electricalfuse. Such a reduction in the electrical current needed for programmingwould allow reduction of the size of a programming transistor.

In view of the above, there exists a need for an electrical fusestructure having improved thermal isolation around a fuselink, andconsequently requiring less programming current, and methods ofmanufacturing the same.

SUMMARY OF THE INVENTION

The present invention addresses the needs described above by providingan electrical fuse having sublithographic cavities on a fuselink,wherein the sublithographic cavities provide enhanced thermal isolationof the fuselink compared with dielectric materials, and methods ofmanufacturing the same.

An electrical fuse is formed on a semiconductor substrate and a firstdielectric layer is formed over the electrical fuse. A dielectrictemplate layer is formed and patterned to form a recessed region over afuselink of the electrical fuse. Self-assembling block copolymerscontaining two or more different polymeric block components that areimmiscible with one another are applied into a recessed regionsurrounded by the dielectric template layer. The self-assembling blockcopolymers are then annealed to form a pattern of multiple circleshaving a sublithographic diameter. The pattern of multiple circles istransferred into the first dielectric layer by a reactive ion etch,wherein the portion of the first dielectric layer above the fuselink hasa honeycomb pattern comprising multiple circular cylindrical holes. Asecond dielectric layer is formed over the circular cylindrical holes bya non-conformal chemical vapor deposition and sublithographic cavitiesare formed on the fuselink. The sublithographic cavities provideenhanced thermal insulation relative to dielectric materials to thefuselink so that the electrical fuse may be programmed with lessprogramming current.

According to an aspect of the present invention, a semiconductorstructure is provided, which comprises:

an electrical fuse comprising a first electrode, a second electrode, anda fuselink, and located on shallow trench isolation in a semiconductorsubstrate, wherein each of the first electrode, the second electrode,and the fuselink comprises a conductive material; and

a plurality of cylindrical cavities located above the fuselink.

According to one embodiment, the plurality of cylindrical cavities has asublithographic diameter, and is separated from the fuselink by asublithographic dimension.

According to another embodiment, the semiconductor structure comprises adielectric spacer abutting outer sidewalls of the first electrode, thesecond electrode, and the fuselink, wherein the plurality of cylindricalholes are located above the dielectric spacer and the shallow trenchisolation.

According to even another embodiment, the plurality of cylindricalcavities is separated from the dielectric spacer and the shallow trenchisolation by the sublithographic dimension.

According to yet another embodiment, each of the plurality ofcylindrical cavities has a cylindrical conical top portion.

According to still another embodiment, the plurality of cylindricalcavities is separated from one another by a first dielectric layerhaving holes arranged in a honeycomb pattern, wherein the plurality ofcylindrical cavities is located within the holes.

According to still yet another embodiment, the semiconductor structurecomprises further comprising a second dielectric layer verticallyabutting the first dielectric layer between the holes, wherein thesecond dielectric layer extends into the holes and encapsulating each ofthe plurality of cylindrical cavities.

According to a further embodiment, the first dielectric layer comprisesa dielectric material selected from the group consisting of a siliconoxide, a silicon nitride, a chemical vapor deposition (CVD) low-kdielectric material, and a spin-on low-k dielectric material.

According to an even further embodiment, the second dielectric layercomprises a dielectric material selected from the group consisting of asilicon oxide, a silicon nitride, and a chemical vapor deposition (CVD)low-k dielectric material.

According to a yet further embodiment, the first dielectric layer andthe second dielectric layer comprise different materials.

According to a still further embodiment, the semiconductor structurefurther comprises a dielectric template layer vertically abutting thefirst dielectric layer and the second dielectric layer and having anopening over the plurality of cylindrical cavities.

According to a yet still further embodiment, the conductive material isa stack of a semiconductor material and a metal semiconductor alloy.

According to further another embodiment, the conductive material is astack of polysilicon and a metal silicide.

According to another aspect of the present invention, a method offorming a semiconductor structure is provided, which comprises:

forming an electrical fuse comprising a first electrode, a secondelectrode, and a fuselink on shallow trench isolation in a semiconductorsubstrate;

forming a first dielectric layer on the electrical fuse;

forming a polymeric matrix comprising a first polymeric block componentand containing cylindrical holes having a sublithographic diameter onthe first dielectric layer;

forming a plurality of cylindrical holes having the sublithographicdiameter in the first dielectric layer by etching the first dielectriclayer; and

depositing a second dielectric layer and forming a plurality ofcylindrical cavities within the cylindrical holes, wherein the seconddielectric layer extends into each of the cylindrical holes andencapsulates the cylindrical cavities.

According to one embodiment, the method further comprises:

applying a block copolymer on the first dielectric layer, wherein theblock copolymer comprises at least the first polymeric block componentand a second polymeric block component that are immiscible with eachother;

annealing the block copolymer to form a plurality of cylindrical blockscomprising the second polymeric block component and having thesublithographic diameter and embedded in the polymeric matrix; and

selectively removing the second polymeric block component relative tothe polymeric matrix.

According to another embodiment, the method further comprises:

forming a dielectric template layer on the first dielectric layer; and

forming an opening having lithographic dimensions in the dielectrictemplate layer over the fuselink.

According to even another embodiment, the depositing of the seconddielectric layer is a non-conformal process that deposits less materialon a lower portion than on a top portion within each of the plurality ofcylindrical holes and forms a conical cavity top.

According to yet another embodiment, the plurality of cylindricalcavities is separated from the fuselink by a sublithographic dimension.

According to still another embodiment, the method further comprisesforming a dielectric spacer directly on sidewalls of the electricalfuse, wherein the plurality of cylindrical cavities is formed above thedielectric spacer and the shallow trench isolation and is separated fromthe dielectric spacer and the shallow trench isolation by portions ofthe second dielectric layer having a sublithographic thickness.

According to still yet another embodiment, the first dielectric layercomprises a first dielectric material selected from the group consistingof a silicon oxide, a silicon nitride, a chemical vapor deposition (CVD)low-k dielectric material, and a spin-on low-k dielectric material, andthe second dielectric layer comprises a second dielectric materialselected from the group consisting of a silicon oxide, a siliconnitride, and a chemical vapor deposition (CVD) low-k dielectricmaterial.

According to a further embodiment, the sublithographic diameter is fromabout 10 nm to about 40 nm.

According to an even further embodiment, the block copolymer comprisesthe first and second polymeric block components, respectively, at aweight ratio of from about 80:20 to about 60:40.

According to a yet further embodiment, each of the plurality ofcylindrical blocks has a substantially horizontal top surface and asubstantially horizontal bottom surface.

According to a still further embodiment, the block copolymer is selectedfrom the group consisting of polystyrene-block-polymethylmethacrylate(PS-b-PMMA), polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-b-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA).

According to a still yet further embodiment, the block copolymercomprises PS-b-PMMA having a PS:PMMA weight ratio ranging from about80:20 to about 60:40.

According to a further another embodiment, the annealing of the blockcopolymer comprises thermal annealing or ultra-violet treatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-7B are sequential views of a first exemplary structureaccording to a first embodiment of the present invention. Figures withthe same numeric label correspond to the same stage of manufacturing;figures with the suffix “A” are top-down views; figures with the suffix“B” are vertical cross-sectional views along the plane B-B′ of thecorresponding figure with the same numeric label and the suffix “A.”

FIG. 8 is a magnified view of a plurality of cylindrical cavities inFIG. 7A.

FIGS. 9A-10B are sequential views of a second exemplary structureaccording to a second embodiment of the present invention. Figures withthe same numeric label correspond to the same stage of manufacturing;figures with the suffix “A” are top-down views; figures with the suffix“B” are vertical cross-sectional views along the plane B-B′ of thecorresponding figure with the same numeric label and the suffix “A.”

DETAILED DESCRIPTION OF THE INVENTION

As stated above, the present invention relates to an electrical fusehaving sublithographic cavities upon a fuselink portion thereof andmethods of manufacturing the same, which are now described in detailwith accompanying figures. It is noted that like and correspondingelements are referred to by like reference numerals.

Referring to FIGS. 1A and 1B, a first exemplary structure according tothe present invention comprises an electrical fuse formed on asemiconductor substrate 8 comprising a substrate layer 10 and shallowtrench isolation 20. Preferably, the entirety of the electrical fuse isformed over the shallow trench isolation 20 and does not abut thesubstrate layer 10 to minimize heat loss during programming.

The electrical fuse comprises a first electrode 51, a second electrode53, and a fuselink 52. Each of the first electrode 51, the secondelectrode 53, and the fuselink 52 comprises a conductive material thatmay be electromigrated. The conductive material may be a metalsemiconductor alloy such as a metal silicide or a metal germanide,and/or a semiconductor material such as silicon, a silicon containingalloy, a germanium containing alloy, a III-V compound semiconductor, ora II-IV semiconductor. Preferably, the conductor material comprises astack of a semiconductor material and a metal semiconductor alloy. Forexample, the conductor material may comprise a stack of polysilicon anda metal silicide. The polysilicon may, or may not, be doped. While thepresent invention is described for a case in which the conductormaterial comprises a stack of a semiconductor material and a metalsemiconductor alloy, embodiments in which the conductive materialconsists of a semiconductor material or a metal semiconductor alloy arealso contemplated herein.

During programming of the electrical fuse (51, 52, 53), a voltage biasis applied across the first electrode 51 and the second electrode 53.The electrode to which a relatively positive bias voltage is appliedduring the programming is typically called an “anode,” while the otherelectrode to which a relatively negative voltage bias is applied iscalled a “cathode.” Thus, one of the first electrode 51 and the secondelectrode 53 is the anode and the other is the cathode.

The first electrode 51 comprises a first electrode semiconductor portion31 and a first electrode metal semiconductor alloy portion 41. Likewise,the second electrode 53 comprises a second electrode semiconductorportion 33 and a second electrode metal semiconductor alloy portion 43.The fuselink 52 comprises a fuselink semiconductor portion 32 and afuselink metal semiconductor alloy portion 42.

The semiconductor substrate 8 may be a bulk substrate, asemiconductor-on-insulator (SOI) substrate, or a hybrid substrate. Thesemiconductor substrate 8 may have a built-in biaxial stress in theplane of the semiconductor substrate 8, i.e., in the plane perpendicularto the surface normal of the top surface of the semiconductor substrate8. While the present invention is described with a bulk substrate,implementation of the present invention on an SOI substrate or on ahybrid substrate is explicitly contemplated herein.

The semiconductor substrate 8 is patterned for a shallow trench andfilled with an insulator material. By planarizing and optionallyrecessing the insulator material, the shallow trench isolation 20 isformed in the semiconductor substrate 8. The portion of thesemiconductor substrate containing a semiconductor material constitutesthe substrate layer 10. The substrate layer 10 may comprise asemiconductor material such as amorphous silicon, epitaxial silicon,single crystal silicon, silicon germanium alloy, silicon carbon alloy,silicon carbon germanium alloy, a III-V compound semiconductor, or aII-VI compound semiconductor. The semiconductor material may besubstantially undoped, doped with p-type dopants, or doped with n-typedopants.

The electrical fuse (51, 52, 53) is typically formed at the same time asa gate stack during processing steps of a semiconductor manufacturingsequence. The gate stack comprises a gate semiconductor material and agate metal semiconductor alloy. While a different semiconductor materialmay be employed for the electrical fuse (51, 52, 53) than the gatesemiconductor material, use of the same semiconducting material for boththe gate semiconductor material and the electrical fuse (51, 52, 53) isin general preferred. Likewise, while a different metal semiconductoralloy material may be employed for the electrical fuse (51, 52, 53) thanthe gate metal semiconductor alloy, use of the same metal semiconductoralloy for both the gate metal semiconductor alloy and the electricalfuse (51, 52, 53) is in general preferred.

The first electrode semiconductor portion 31, the second electrodesemiconductor portion 33, and the fuselink semiconductor portion 32comprise a semiconductor material that may be selected from, but is notlimited to, silicon, germanium, silicon-germanium alloy, silicon carbonalloy, silicon-germanium-carbon alloy, gallium arsenide, indiumarsenide, indium phosphide, III-V compound semiconductor materials,II-VI compound semiconductor materials, organic semiconductor materials,and other compound semiconductor materials. The semiconductor materialmay be doped with electrical dopants, or undoped. The thickness of thevarious semiconductor portions (31, 32, 33) may be from about 10 nm toabout 300 nm, and typically from about 50 nm to about 120 nm, althoughlesser and greater thicknesses are also contemplated herein. Differentportions of the electrical fuse (51, 52, 53) may comprise semiconductormaterials having different dopants.

Each of the first electrode metal semiconductor alloy portion 41, thesecond electrode metal semiconductor alloy portion 43, and the fuselinkmetal semiconductor alloy portion 42 comprises a metal semiconductoralloy. In case the first electrode semiconductor portion 31, the secondelectrode semiconductor portion 33, and the fuselink semiconductorportion 32 comprise silicon, the first electrode metal semiconductoralloy portion 41, the second electrode metal semiconductor alloy portion44, and the fuselink metal semiconductor alloy portion 43 may comprise ametal silicide such as nickel silicide (NiSi_(x)), cobalt silicide(CoSi_(x)), tantalum silicide (TaSi_(x)), and titanium silicide(TiSi_(x)), tungsten silicide (WSi_(x)), platinum silicide (PtSi_(x)) oralloys thereof. The value of x is in general between 1 and 3. A metalnitride such as TaN_(x), TiN_(x), or WN_(x) may be employed instead of ametal silicide as well.

A dielectric material is conformally deposited on sidewalls of theelectrical fuse (51, 52, 53) and etched by a reactive ion etch to from adielectric spacer 34. The dielectric spacer 34 abuts sidewalls of theelectrical fuse (51, 52, 53), i.e., sidewalls of the first electrode 51,the second electrode 52, and the fuselink 52. The dielectric spacer 34surrounds the electrical fuse (51, 52, 53) and is topologicallyhomomorphic to a torus, i.e., may be continuously stretched and bentinto a torus.

Referring to FIGS. 2A and 2B, a first dielectric layer 36 comprising afirst dielectric material is formed on the electrical fuse (51, 52, 53).The first dielectric layer 36 abuts the top surfaces of the electricalfuse (51, 52, 53) and the sidewall of the dielectric spacer 34. Thefirst dielectric material may comprise a silicon oxide, a siliconnitride, a chemical vapor deposition (CVD) low-k dielectric material, ora spin-on low-k dielectric material.

Non-limiting examples of the silicon oxide include undoped silicateglass (USG), borosilicate glass (BSG), phosphosilicate glass (PSG),borophosphosilicate glass (BPSG), fluorosilicate glass (FSG), and TEOS(tetra-ethyl-ortho-silicate) oxide. The silicon nitride may be astoichiometric nitride, or a non stoichiometric nitride applying atensile or compressive stress to underlying structures.

The CVD low-k dielectric material may be a SiCOH dielectric containing amatrix of a hydrogenated oxidized silicon carbon material (SiCOH)comprising atoms of Si, C, O and H in a covalently bondedtri-dimensional network. The CVD low-k dielectric material can be porousor nonporous. Such CVD low-k dielectric material has a dielectricconstant of not more than about 2.8 and typically comprises betweenabout 5 and about 40 atomic percent of Si; between about 5 and about 45atomic percent of C; between 0 and about 50 atomic percent of O; andbetween about 10 and about 55 atomic percent of H. The tri-bondednetwork may include a covalently bonded tri-dimensional ring structurecomprising Si—O, Si—C, Si—H, C—H and C—C bonds. Further, the CVD low-kdielectric material may comprise F and N and may optionally have the Siatoms partially substituted by Ge atoms. The CVD low-k dielectricmaterial may contain molecular scale voids (i.e., nanometer-sized pores)of between about 0.3 to about 50 nanometers in diameter, and mostpreferably between about 0.4 and about 10 nanometers in diameter,further reducing the dielectric constant of the first dielectric layer36 to values below about 2.0.

The spin-on low-k dielectric material has a dielectric constant of about3.0 or less, preferably less than about 2.8, and more preferably lessthan about 2.5. The spin-on low-k dielectric material can be porous ornonporous. An example of the spin-on low-k dielectric material is athermosetting polyarylene ether, which is also commonly referred to as“Silicon Low-K”, or “SiLK.” The term “polyarylene” denotes aryl moietiesor inertly substituted aryl moieties which are linked together by bonds,fused rings, or inert linking groups such as oxygen, sulfur, sulfone,sulfoxide, carbonyl, etc.

The first dielectric layer 36 may be self-planarizing as in the case ofthe spin-on low-k dielectric material, or may be planarized as needed.Typical thickness of the first dielectric layer 36 as measured from atop surface of the semiconductor substrate 8, i.e., from the interfacebetween the shallow trench isolation and the electrical fuse (51, 52,53), may be from about 200 nm to about 600 nm, and typically from about300 nm to about 450 nm.

A dielectric template layer 40 is deposited on the first dielectriclayer 40. The thickness of the dielectric template layer 40 may be fromabout 30 nm to about 300 nm, and typically from about 50 nm to about 200nm. The dielectric template layer 40 may comprise a silicon oxide, asilicon nitride, or a stack thereof.

A photoresist (not shown) is applied on the dielectric template layer 40and lithographically patterned to expose the portion of the dielectrictemplate layer 40 over the fuselink 52. An opening having a lithographicdimension is patterned in the photoresist. The opening may be ellipticalor rectangular. In case the opening is elliptical, the lengths of majoraxis and the minor axis of the ellipse are lithographic dimensions. Theopening may be a circle, in which case the major and minor axes are thesame and is a diameter of a circle. In case the opening is rectangular,the length and width of the rectangle are lithographic dimensions.

The pattern of the opening in the photoresist is transferred into thedielectric template layer 40 by a reactive ion etch. Thus, thedielectric template layer 40 contains an opening having a lithographicdimension located over the fuselink 52. The opening may be located aboveportions of the dielectric spacer 34 abutting the fuselink 52 andportions of the shallow trench isolation 20 adjacent to the dielectricspacer 34. In one case, the opening may be rectangular, and the width ofthe opening, or the dimension of the opening in the directionperpendicular to the direction from the first electrode 51 to the secondelectrode 53, may be less than the width of the fuselink, i.e., thedimension of the fuselink 52 in the direction perpendicular to thedirection from the first electrode 51 to the second electrode 53, sothat the rectangle overlaps a portion of the fuselink 52 but does notoverlap the dielectric spacer 34 in a see-through top-down view. Inanother case, the width of the opening may be greater than the width ofthe fuselink 52 and less than the sum of the width of the fuselink 52and twice the width of the dielectric spacer 34, so that the rectangleoverlaps a portion of the fuselink 52 and portions of the dielectricspacer 34 in a see-through top-down view. In still another case, thewidth of the rectangle may be greater than the sum of the width of thefuselink 52 and twice the width of the dielectric spacer 34 so that therectangle overlaps a portion of the fuselink 52, portions of thedielectric spacer 34, and portions of the shallow trench isolation 20 ina see-through top-down view.

Referring to FIGS. 3A and 3B, a block copolymer mixture comprisingself-assembling block copolymers that are capable of self-organizinginto nanometer-scale patterns is applied over the first dielectric layer36 within the opening in the dielectric template layer 40 to form ablock copolymer layer 50. The block copolymer comprises at least a firstpolymeric block component and a second polymeric block component thatare immiscible with each other. Under suitable conditions, the two ormore immiscible polymeric block components separate into two or moredifferent phases on a nanometer scale and thereby form ordered patternsof isolated nano-sized structural units. Such ordered patterns ofisolated nano-sized structural units formed by the self-assembling blockcopolymers can be used for fabricating nano-scale structural units insemiconductor, optical, and magnetic devices. Specifically, dimensionsof the structural units so formed are typically in the range of 10 to 40nm, which are sub-lithographic (i.e., below the resolutions of thelithographic tools).

While a “lithographic minimum dimension” and a “sublithographicdimension” are defined only in relation to a lithography tool andnormally changes from generation to generation of semiconductortechnology, it is understood that the lithographic minimum dimension andthe sublithographic dimension are to be defined in relation to the bestperformance of lithography tools available at the time of semiconductormanufacturing. As of 2007, the lithographic minimum dimension is about50 nm and is expected to shrink in the future.

Exemplary materials for the block copolymer layer 50 are described incommonly-assigned, copending U.S. patent application Ser. No.11/424,963, filed on Jun. 19, 2006, the contents of which areincorporated herein by reference. Specific examples of self-assemblingblock copolymers that can be used for forming the structural units ofthe present invention may include, but are not limited to:polystyrene-block-polymethylmethacrylate (PS-b-PMMA),polystyrene-block-polyisoprene (PS-b-PI),polystyrene-block-polybutadiene (PS-b-PBD),polystyrene-block-polyvinylpyridine (PS-b-PVP),polystyrene-block-polyethyleneoxide (PS-b-PEO),polystyrene-block-polyethylene (PS-b-PE),polystyrene-b-polyorganosilicate (PS-b-POS),polystyrene-block-polyferrocenyldimethylsilane (PS-b-PFS),polyethyleneoxide-block-polyisoprene (PEO-b-PI),polyethyleneoxide-block-polybutadiene (PEO-b-PBD),polyethyleneoxide-block-polymethylmethacrylate (PEO-b-PMMA),polyethyleneoxide-block-polyethylethylene (PEO-b-PEE),polybutadiene-block-polyvinylpyridine (PBD-b-PVP), andpolyisoprene-block-polymethylmethacrylate (PI-b-PMMA). Theself-assembling block copolymers are first dissolved in a suitablesolvent system to form a block copolymer solution, which is then appliedonto the surface of the first exemplary structure to form the blockcopolymer layer 50. The solvent system used for dissolving the blockcopolymer and forming the block copolymer solution may comprise anysuitable solvent, including, but not limited to: toluene, propyleneglycol monomethyl ether acetate (PGMEA), propylene glycol monomethylether (PGME), and acetone.

For example, the block copolymer may comprise the first and secondpolymeric block components, respectively, at a weight ratio of fromabout 80:20 to about 60:40. The block copolymer may comprise PS-b-PMMAhaving a PS:PMMA weight ratio ranging from about 80:20 to about 60:40.

Referring to FIGS. 4A and 4B, the first exemplary semiconductorstructure is annealed by ultraviolet treatment or by thermal annealingat an elevated temperature to form a plurality of cylindrical blocks 51comprising the second polymeric block component, having a firstsublithographic diameter d1, and embedded in the polymeric matrix 52that comprises the first polymeric block component. Each of theplurality of cylindrical blocks 51 has a substantially horizontal topsurface and a substantially horizontal bottom surface.

Exemplary processes of annealing the self-assembling block copolymers inthe block copolymer layer 50 to form two sets of polymer blocks aredescribed in Nealey et al., “Self-assembling resists fornanolithography,” IEDM Technical Digest, December, 2005, Digital ObjectIdentifier 10.1109/IEDM.2005.1609349, the contents of which areincorporated herein by reference. Further, methods of annealingdescribed in the '963 application may be employed. The anneal may beperformed, for example, at a temperature from about 200° C. to about300° C. for a duration from less than about 1 hour to about 100 hours.

Referring to FIGS. 5A and 5B, the plurality of cylindrical blocks 51comprising the second polymeric block component is selectively removingrelative to the polymeric matrix 52 comprising the first polymeric blockcomponent. The polymeric matrix 52 has a honeycomb pattern, and containscylindrical holes having the first sublithographic diameter d1.

The honeycomb pattern in the polymeric matrix 52 is then transferredinto the first dielectric layer 36 by an anisotropic reactive ion etchthat employs the polymeric matrix 52 as an etch mask. A plurality ofcylindrical holes having the first sublithographic diameter d1 is formedin the first dielectric layer 36. Preferably, the anisotropic reactiveion etch is selective to the fuselink 52, the dielectric spacer 34, andthe shallow trench isolation 20. In case the fuselink 52 comprises thefuselink metal semiconductor alloy 42, the anisotropic ion etch isselective to the fuselink metal semiconductor alloy 42.

Portions of the fuselink metal semiconductor alloy 42 are exposed at thebottom of some cylindrical holes. Depending on the dimensions of theopening in the dielectric template layer 40, portions of the dielectricspacer 34 may be exposed at the bottom of some other cylindrical holes.Depending on the dimensions of the opening in the dielectric templatelayer 40, portions of the shallow trench isolation 20 may be exposed atthe bottom of still other cylindrical holes.

Referring to FIGS. 6A and 6B, the polymeric matrix 52 is removed, forexample, by ashing or by a wet etch. The first dielectric layer 36 has aplurality of cylindrical holes having the first sublithographic diameterd1 and arranged in a honeycomb pattern above the fuselink 52. Since thediameter d1 of the plurality of cylindrical holes is sublithographic,e.g., less than 50 nm, while the height of the cylindrical holes in thefirst dielectric layer 36 is typically from about 150 nm to about 400nm, the aspect ratio of each of the cylindrical holes in the firstdielectric layer 36 is greater than 3, and typically from about 4 toabout 30.

Referring to FIGS. 7A and 7B, a second dielectric layer 70 is depositedon the first dielectric layer 36. The second dielectric layer 70 maycomprise a silicon oxide, a silicon nitride, or a chemical vapordeposition (CVD) low-k dielectric material. Exemplary materials for thesilicon oxide, the silicon nitride, and the CVD low-k dielectricmaterial are as described above.

The second dielectric layer 70 is deposited by a non-conformaldeposition, i.e., the deposition process is depletive and mass flowlimited. The second dielectric material may, or may not be, the samematerial as the first dielectric material. Sine each of the cylindricalholes in the first dielectric layer 36 has a high aspect ratio, only athin layer of second dielectric material is deposited on the sidewallsand bottom surfaces of the cylindrical holes in the first dielectriclayer 36, while the top surface of the first dielectric layer 36accumulates a second dielectric material to cover the cylindrical holesin the first dielectric layer 36. Cylindrical cavities CC that areencapsulated, i.e., completely surrounded without any opening, by thesecond dielectric material is formed within each of the plurality ofcylindrical holes in the first dielectric layer 36. The seconddielectric material extends into each of the cylindrical holes withinthe first dielectric layer 36 and encapsulates each of the cylindricalcavities. The diameter of the cylindrical cavities, defined as anaverage diameter of substantially cylindrical portion of the cylindricalcavities CC, is a second sublithographic diameter d2, which is less thanthe first sublithographic diameter d1. The cylindrical cavities CC aresublithographic cylindrical cavities, i.e., cylindrical cavities havinga sublithographic dimension, which is the second sublithographicdiameter d2.

Near the top of the cylindrical holes in the first dielectric layer 36,the thickness of the second dielectric material on the sidewalls of thecylindrical holes increases with height until the cylindrical cavitiesnarrow down to a point. The top portion of each of the cylindricalcavities has a substantially conical shape, i.e., each of thecylindrical cavities has a cylindrical conical top portion. The apex ofeach of the cylindrical cavities coincides with the center of across-sectional area of the cylindrical cavity CC as seen in asee-through top-down view.

Referring to FIG. 8, a magnified view of the vertical cross-sectionalview of FIG. 7A is shown. Due to the non-conformal nature of thedeposition process for the second dielectric layer 70, the thickness t1of the second dielectric material between the fuselink metalsemiconductor alloy 32 and each of the cylindrical cavities CC issublithographic. The thickness t1 may be typically from about 0.5 nm toabout 10 nm. The first sublithographic diameter d1 may be typically fromabout 10 nm to about 40 nm. The difference between the firstsublithographic diameter d1 and the second sublithographic diameter d2may be from about 0.5 nm to about 10 nm.

The plurality of cylindrical cavities CC provides enhanced thermalinsulation to the fuselink 52 than any dielectric material sincevirtually no heat flows through the cylindrical cavities by conduction.Thus, the fuselink 52 is better thermally insulated from surroundingstructures and capable of maintaining a higher temperature duringprogramming of the electrical fuse (51, 52, 53). A more reliableprogramming may be performed at a higher temperature than conventionalelectrical fuses employing thermal insulation by a dielectric materialwithout cavities. Alternatively, a smaller programming current may besupplied from a smaller programming transistor so that the temperatureduring programming is comparable with the temperature during programmingof a conventional electrical fuse that does not have a cavity thereupon.The smaller programming transistor has a less footprint than aconventional programming transistor.

In addition, the thin portion of the second dielectric material locateddirectly above the fuselink 52 and having the thickness t1 may be easilybroken to relieve pressure in the fuselink 52 that may build up duringelectromigration. Thus, the cylindrical cavities CC serve as a reservoirof volume into which an electromigrated material from the fuselink 52may flow during programming of the electrical fuse (51, 52, 53) torelieve pressure during the electromigration process, thus facilitatingthe electromigration of the material in the fuselink 52.

Referring to FIGS. 9A and 9B, a second exemplary structure according toa second embodiment of the present invention is derived from the firstexemplary structure shown in FIGS. 6A and 6B by removing the templatedielectric layer 40 selective to the first dielectric layer 36. In thesecond embodiment, the template dielectric layer 40 comprises adifferent material than the first dielectric layer 36. A reactive ionetch or a wet etch process that etches the template dielectric materiallayer 40 selective to the first dielectric layer 36 may be employed.

Referring to FIGS. 10A and 10B, a second dielectric layer is depositedon the first dielectric layer as in the processing step corresponding toFIGS. 7A and 7B in the first embodiment. The same second dielectricmaterial and the same process may be employed as in the first embodimentto form the cylindrical cavities CC having the same structuralcharacteristics as in the first embodiment. However, the secondexemplary semiconductor structure does not contain a template dielectriclayer.

While the invention has been described in terms of specific embodiments,it is evident in view of the foregoing description that numerousalternatives, modifications and variations will be apparent to thoseskilled in the art. Accordingly, the invention is intended to encompassall such alternatives, modifications and variations which fall withinthe scope and spirit of the invention and the following claims.

1. A semiconductor structure comprising: an electrical fuse comprising afirst electrode, a second electrode, and a fuselink, and located onshallow trench isolation in a semiconductor substrate, wherein each ofsaid first electrode, said second electrode, and said fuselink comprisesa conductive material; and a plurality of cylindrical cavities locatedabove said fuselink.
 2. The semiconductor structure of claim 1, whereinsaid plurality of cylindrical cavities has a sublithographic diameter,and is separated from said fuselink by a sublithographic dimension. 3.The semiconductor structure of claim 2, further comprising a dielectricspacer abutting outer sidewalls of said first electrode, said secondelectrode, and said fuselink, wherein said plurality of cylindricalholes are located above said dielectric spacer and said shallow trenchisolation.
 4. The semiconductor structure of claim 3, wherein saidplurality of cylindrical cavities is separated from said dielectricspacer and said shallow trench isolation by said sublithographicdimension.
 5. The semiconductor structure of claim 1, wherein each ofsaid plurality of cylindrical cavities has a cylindrical conical topportion.
 6. The semiconductor structure of claim 1, wherein saidplurality of cylindrical cavities is separated from one another by afirst dielectric layer having holes arranged in a honeycomb pattern,wherein said plurality of cylindrical cavities are located within saidholes.
 7. The semiconductor structure of claim 6, further comprising asecond dielectric layer vertically abutting said first dielectric layerbetween said holes, wherein said second dielectric layer extends intosaid holes and encapsulating each of said plurality of cylindricalcavities.
 8. The semiconductor structure of claim 7, wherein said firstdielectric layer comprises a dielectric material selected from the groupconsisting of a silicon oxide, a silicon nitride, a chemical vapordeposition (CVD) low-k dielectric material, and a spin-on low-kdielectric material.
 9. The semiconductor structure of claim 7, whereinsaid second dielectric layer comprises a dielectric material selectedfrom the group consisting of a silicon oxide, a silicon nitride, and achemical vapor deposition (CVD) low-k dielectric material.
 10. Thesemiconductor structure of claim 7, wherein said first dielectric layerand said second dielectric layer comprise different materials.
 11. Thesemiconductor structure of claim 7, further comprising a dielectrictemplate layer vertically abutting said first dielectric layer and saidsecond dielectric layer, and having an opening over said plurality ofcylindrical cavities.
 12. The semiconductor structure of claim 1,wherein said conductive material is a stack of a semiconductor materialand a metal semiconductor alloy.
 13. The semiconductor structure ofclaim 12, wherein said conductive material is a stack of polysilicon anda metal silicide.
 14. A method of forming a semiconductor structurecomprising: forming an electrical fuse comprising a first electrode, asecond electrode, and a fuselink on shallow trench isolation in asemiconductor substrate; forming a first dielectric layer on saidelectrical fuse; forming a polymeric matrix comprising a first polymericblock component and containing cylindrical holes having asublithographic diameter on said first dielectric layer; forming aplurality of cylindrical holes having said sublithographic diameter insaid first dielectric layer by etching said first dielectric layer; anddepositing a second dielectric layer and forming a plurality ofcylindrical cavities within said cylindrical holes, wherein said seconddielectric layer extends into each of said cylindrical holes andencapsulates said cylindrical cavities.
 15. The method of claim 14,further comprising: applying a block copolymer on said first dielectriclayer, wherein said block copolymer comprises at least said firstpolymeric block component and a second polymeric block component thatare immiscible with each other; annealing said block copolymer to form aplurality of cylindrical blocks comprising said second polymeric blockcomponent and having said sublithographic diameter and embedded in saidpolymeric matrix; and selectively removing said second polymeric blockcomponent relative to said polymeric matrix.
 16. The method of claim 15,further comprising: forming a dielectric template layer on said firstdielectric layer; and forming an opening having lithographic dimensionsin said dielectric template layer over said fuselink.
 17. The method ofclaim 14, wherein said depositing of said second dielectric layer is anon-conformal process that deposits less material on a lower portionthan on a top portion within each of said plurality of cylindrical holesand forms a conical cavity top.
 18. The method of claim 14, wherein saidplurality of cylindrical cavities is separated from said fuselink by asublithographic dimension.
 19. The method of claim 14, furthercomprising forming a dielectric spacer directly on sidewalls of saidelectrical fuse, wherein said plurality of cylindrical cavities isformed above said dielectric spacer and said shallow trench isolationand is separated from said dielectric spacer and said shallow trenchisolation by portions of said second dielectric layer having asublithographic thickness.
 20. The method of claim 14, wherein saidfirst dielectric layer comprises a first dielectric material selectedfrom the group consisting of a silicon oxide, a silicon nitride, achemical vapor deposition (CVD) low-k dielectric material, and a spin-onlow-k dielectric material, and said second dielectric layer comprises asecond dielectric material selected from the group consisting of asilicon oxide, a silicon nitride, and a chemical vapor deposition (CVD)low-k dielectric material.